The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as active fuel management (AFM). Operation using all of the engine cylinders is referred to as an “activated” mode (AFM disabled). A “deactivated” mode (AFM enabled) refers to operation using less than all of the cylinders of the engine (one or more cylinders not active).
In the deactivated mode, there are fewer cylinders operating. Nonetheless, there can still be adequate drive torque available to drive the vehicle driveline (such as during cruise control) and accessories (e.g., alternator, coolant pump, A/C compressor). Engine efficiency, however, is increased as a result of less engine pumping loss and higher combustion efficiency. The pumping loss experienced by the engine is mainly due to the flow restriction for flow into and out of the cylinders. The quantity of air and/or the composition/quality of gas in the cylinder can play minimum role to pumping loss during compression and expansion processes because the compression work (−) and the expansion work (+) will be traded.
Cruise control systems can be provided for maintaining a vehicle at a fixed operating speed. In some instances, a vehicle can be operating in a “deactivated” mode (AFM enabled) while cruise control is engaged. As is typical however, it may be necessary for the engine control system to command a torque increase in order to maintain the fixed operating speed due to outside influences (such as encountering a hill, etc.). As a result, AFM typically would transition to a disabled state to provide the required torque (i.e., to the “activated” mode).